OTOSCLEROSIS IN THE INCUS

Abstract

To the Editor: The last issue of the journal (Otology & Neurotology, 28:301-3) published a paper titled "Otosclerosis of the Incus." Escada et al. (1) describes a bony lesion in the incus that is considered to be otosclerotic upon hematoxylin-eosin staining and a single light microscopic histological examination (1). A series of articles have been published during the last 3 years about the pathogenesis of otosclerosis (Karosi et al. 2-4). These reports clearly call the attention to the fact that all histologically otosclerotic stapes fixations are associated with the presence of measles virus genomic RNA. Otosclerotic stapes fixations are, however, only two thirds of the stapes fixations in a series of more than 300 stapes footplates consecutively operated on during the last 4 years (3,4). Similar histological lesions and/or presence of measles virus in the stapes superstructure or other bones are not found. Those ankylotic stapes that do not represent otosclerosis show heterogeneous histological pattern of localized hemosiderosis, lymphocytic-plasmocytic infiltration with thickened stapedial mucosal layer, globular fibrosis, or annular calcification (3,4). The otic capsule shows inevitable affinity to persisting measles virus infection and replication, which coincides with the organ-specific localization of otosclerotic foci. The subsequent inflammatory process is characterized by pseudovascular, irregular, and hypercellular absorption lacunae bordered by numerous osteoclasts and multi-nucleated giant cells in the active stage. In contrast, the inactive phase of otosclerosis is featured by almost total absence of bone-derived cells with woven and mosaiclike pattern of cement lines. In these cases, the osteoid substance represents homogeneous eosinophilia. Nevertheless, cement lines cannot be visualized without polarizing light microscopic analysis (3,4), and cement line pattern is a structure of inorganic bony material that is not identical with the osteoid rings bordered by osteocytes. The presented histological section of the incus in the cited article shows no sign of the aforementioned histological features; rather, it shows regular vascular cross sections and Haversian lacunae (1). The section shows normal cellularity and concentric disposition of regular osteocytes. No osteoclasts or giant cells can be identified. The osteoid substance is eosinophilic, only the bulky perivascular connective tissue and vascular endothelial cells are characterized by basophilia. It does not represent information about the pattern of osteoid cement lines. It would be helpful to identify the sectioned part of the incus because intraosseal vascular network is different in the long process and in the body. In addition, the serological diagnosis of otosclerosis is based upon the antimeasles immunoglobulin G low concentration (<12 IU/mL) in the sera of these patients versus healthy immunized individuals' high titer (>100 IU/mL) (5). The specificity and sensitivity of this test for otosclerosis in conductive hearing loss are around 95% (5). Today, we do think, that the diagnosis of otosclerosis cannot be established without detecting low antimeasles immunoglobulin G in the serum and/or detecting measles virus RNA in the affected bone specimen. István Sziklai, M.D., D.Sc. Tamás Karosi, M.D., Ph.D. Department of Otolaryngology- Head and Neck Surgery University Medical School of Debrecen Debrecen, Hungary